Within the power industry, valves are operated remotely from open, closed and intermediate positions to improve or maintain utility power plant output, or in many cases to provide for the protection of the general public from release of radioactive materials either directly or indirectly. Continual, proper operation of these valves is essential to the well-being of the industry and the general public. The extreme emphasis on safety in nuclear power plants (and the presently bad reputation of the nuclear industry) has put a premium on the importance of maintaining proper operation of valves, of which there may be hundreds within a single plant.
At the forefront of industry attempts to monitor and maintain proper operation of these critical valves is the recent invention of Arthur G. Charbonneau, et. al. described in U.S. Pat. No. 4,542,649 (hereinafter referred to as .-+.649"). The 649 invention disclosed a new and important valve operator monitoring system to measure, record and correlate valve stem load, limit and torque switch positions, spring pack movement and motor current providing time related information on valve performance. The information made available by the 649 patent provides a direct indication of developing valve and operator problems such as excessive or inadequate packing load, excessive inertia, proximity to premature tripping, incorrectly set operating limit and torque switches, improperly functioning thermal overload devices, inadequate or excessive stem thrust loads, gear train wear, stem damage, and load relaxation.
Although the 649 patent provides very valuable information relating to the valve operator and its surrounding systems, the 649 patent does not provide direct measurements or records as to the torque; nor does the 649 patent correlate torque measurements to other parameters within the valve operator system, such as torque switch settings, motor current and spring pack movement. Rather, in the 649 patent, the switch settings, motor current and spring pack movement are related to the thrust, also known as force or stem load, delivered by the valve operator. The 649 patent does not provide direct relationships between those important valve operator characteristics which are directly related to system torque.
Without a proper understanding of valve operator torque outputs, there is no way of verifying that the operator is providing the originally specified torque for given settings of the operator's torque tripped safety switches. Failure to provide proper, specified torque, could result from improper switch settings, physical problems with the spring pack installation or function of the spring pack or improper installation of the torque switches. If these valve operator problems remain undetected, the results could be such difficulties as breakage of a valve due to too much torque, failure of a valve to sufficiently close due to too little torque, and failure of the valve to properly react to or complete its function in an emergency situation. All of these, and othe related problems, can be extremely detrimental, especially in nuclear reactor plants.